Most commonly employed bacterial strains for use in mutagenicity testing are provided in convenient lyophilized disc format. Some strains are not amenable to freeze drying and are offered either suspended in transport medium or frozen. Strains are periodically characterized and verified for diagnostic performance. Confirmed strains are lyophilized in modified ATCC Reagent 18, suspended in transport medium (73-1535psk), or frozen (TAMix). After preservation, samples are cultured and their phenotypes and responses to diagnostic mutagens are determined. Strains are accompanied by Quality Control statements that include the results of phenotype confirmation tests, diagnostic mutagen response and viability assessment. Culture instructions are included with the QC Statement. The bacterial strains contained in STDiscs™ and ECDiscs™ are potential etiologic agents and are intended for use only by those skilled in the safe handling of potentially infectious agents.